displ macro opr   ; 定义宏displ
    mov ah, 2
    mov dl, opr
    int 21h
endm

.model small
.data
time1 db ?
time2 db ?
n db 4
.code
start:
    mov ax, @data
    mov ds, ax
lll:
    mov al, n      
    out 70h, al
    in al, 71h
    mov ah, al
    mov cl, 4
    shr ah, cl
    add ah, 30h
    and al, 0fh
    add al, 30h
    mov time1, ah
    mov time2, al
    displ time1
    displ time2
    sub n, 2
    js exit
    displ ':'
    jmp lll
exit:
    mov ah, 4ch
    int 21h
end start